Godot Mono/.NET Install Script for linux

Adapted from SingingBush/godot-fedora.md.

Prerequisites

Mono (Required for Godot)
- Debian-based instructions
- Arch: mono
- Fedora: mono-devel
ImageMagick (Required for the script. Could already be installed since it is a popular dependancy)
- Debian-based: imagemagick
- Arch: imagemagick
- Fedora: ImageMagick

Recommended (Unsure if it is necesarry)

.NET (Latest version is 8.0 as of latest commit)

The command is the same for every package manager and follows the format dotnet-sdk-<version>. It's available on the following the distos using the latest version as an example.
- Debian-based: dotnet-sdk-8.0
- Arch AUR: dotnet-sdk-8.0
- Fedora: dotnet-sdk-8.0

This script only works for v4.2.1 and acts as a first time install as it downloads an icon and creates a launcher.

I hope to make this work as an update script as well.